Buggy code:
} ; private static final Scheme SLOW_HTTP ; private static final HttpParams DEFAULT_HTTP_PARAMS ; private static final String USER_TOKEN = "__jmeter.USER_TOKEN__" ; private volatile HttpUriRequest currentRequest ; private volatile boolean resetSSLContext ; protected HTTPHC4Impl ( HTTPSamplerBase testElement ) { } public static final class HttpDelete extends HttpEntityEnclosingRequestBase { public HttpDelete ( final URI uri ) { } @ Override public String getMethod ( ) { } } @ Override protected HTTPSampleResult sample ( URL url , String method , boolean areFollowingRedirect , int frameDepth ) { } private void extractClientContextAfterSample ( HttpContext localContext ) { } private void setupClientContextBeforeSample ( HttpContext localContext ) { } protected void handleMethod ( String method , HTTPSampleResult result , HttpRequestBase httpRequest , HttpContext localContext ) throws IOException { } protected HTTPSampleResult createSampleResult ( URL url , String method ) { } private HttpResponse executeRequest ( final HttpClient httpClient , final HttpRequestBase httpRequest , final HttpContext localContext , final URL url ) throws IOException , ClientProtocolException { } private static final class HttpClientKey { private final String target ; private final boolean hasProxy ; private final String proxyHost ; private final int proxyPort ; private final String proxyUser ; private final String proxyPass ; private final int hashCode ; public HttpClientKey ( URL url , boolean hasProxy , String proxyHost , int proxyPort , String proxyUser , String proxyPass ) { } private int getHash ( ) { } private int getHash ( String s ) { } @ Override public boolean equals ( Object obj ) { } @ Override public int hashCode ( ) { } @ Override public String toString ( ) { } } private HttpClient setupClient ( URL url , SampleResult res ) { Map < HTTPHC4Impl . HttpClientKey , HttpClient > mapHttpClientPerHttpClientKey = HTTPHC4Impl . HTTPCLIENTS_CACHE_PER_THREAD_AND_HTTPCLIENTKEY . get ( ) ; final String host = url . getHost ( ) ; String proxyHost = getProxyHost ( ) ; int proxyPort = getProxyPortInt ( ) ; String proxyPass = getProxyPass ( ) ; String proxyUser = getProxyUser ( ) ; boolean useStaticProxy = isStaticProxy ( host ) ; boolean useDynamicProxy = isDynamicProxy ( proxyHost , proxyPort ) ; boolean useProxy = useStaticProxy || useDynamicProxy ; if ( ! useDynamicProxy ) { proxyHost = PROXY_HOST ; proxyPort = PROXY_PORT ; proxyUser = PROXY_USER ; proxyPass = PROXY_PASS ; } HTTPHC4Impl . HttpClientKey key = new HTTPHC4Impl . HttpClientKey ( url , useProxy , proxyHost , proxyPort , proxyUser , proxyPass ) ; HttpClient httpClient = mapHttpClientPerHttpClientKey . get ( key ) ; if ( ( ( httpClient != null ) && ( resetSSLContext ) ) && ( PROTOCOL_HTTPS . equalsIgnoreCase ( url . getProtocol ( ) ) ) ) { ( ( AbstractHttpClient ) ( httpClient ) ) . clearRequestInterceptors ( ) ; ( ( AbstractHttpClient ) ( httpClient ) ) . clearResponseInterceptors ( ) ; httpClient . getConnectionManager ( ) . closeIdleConnections ( 1L , TimeUnit . MICROSECONDS ) ; httpClient = null ; JsseSSLManager sslMgr = ( ( JsseSSLManager ) ( SSLManager . getInstance ( ) ) ) ; sslMgr . resetContext ( ) ; resetSSLContext = false ; } if ( httpClient == null ) { HttpParams clientParams = new org . apache . http . params . DefaultedHttpParams ( new BasicHttpParams ( ) , HTTPHC4Impl . DEFAULT_HTTP_PARAMS ) ; DnsResolver resolver = this . testElement . getDNSResolver ( ) ; if ( resolver == null ) { <START_BUG> resolver = new SystemDefaultDnsResolver ( ) ; <END_BUG> } ClientConnectionManager connManager = new MeasuringConnectionManager ( HTTPHC4Impl . createSchemeRegistry ( ) , resolver ) ; httpClient = new DefaultHttpClient ( connManager , clientParams ) { @ Override protected HttpRequestRetryHandler createHttpRequestRetryHandler ( ) { return new DefaultHttpRequestRetryHandler ( HTTPHC4Impl . RETRY_COUNT , false ) ; } } ; if ( ( HTTPHC4Impl . IDLE_TIMEOUT ) > 0 ) { ( ( AbstractHttpClient ) ( httpClient ) ) . setKeepAliveStrategy ( HTTPHC4Impl . IDLE_STRATEGY ) ; } ( ( AbstractHttpClient ) ( httpClient ) ) . addResponseInterceptor ( new ResponseContentEncoding ( ) ) ; ( ( AbstractHttpClient ) ( httpClient ) ) . addResponseInterceptor ( HTTPHC4Impl . METRICS_SAVER ) ; ( ( AbstractHttpClient ) ( httpClient ) ) . addRequestInterceptor ( HTTPHC4Impl . METRICS_RESETTER ) ; SchemeRegistry schemeRegistry = httpClient . getConnectionManager ( ) . getSchemeRegistry ( ) ; if ( ( HTTPHC4Impl . SLOW_HTTP ) != null ) { schemeRegistry . register ( HTTPHC4Impl . SLOW_HTTP ) ; } if ( useProxy ) { HttpHost proxy = new HttpHost ( proxyHost , proxyPort ) ; clientParams . setParameter ( DEFAULT_PROXY , proxy ) ; if ( ( proxyUser . length ( ) ) > 0 ) { ( ( AbstractHttpClient ) ( httpClient ) ) . getCredentialsProvider ( ) . setCredentials ( new AuthScope ( proxyHost , proxyPort ) , new org . apache . http . auth . NTCredentials ( proxyUser , proxyPass , localHost , PROXY_DOMAIN ) ) ; } } clientParams . setParameter ( COOKIE_POLICY , IGNORE_COOKIES ) ; if ( HTTPHC4Impl . log . isDebugEnabled ( ) ) { HTTPHC4Impl . log . debug ( ( ( ( "Created<seq2seq4repair_space>new<seq2seq4repair_space>HttpClient:<seq2seq4repair_space>@" + ( System . identityHashCode ( httpClient ) ) ) + "<seq2seq4repair_space>" ) + ( key . toString ( ) ) ) ) ; } mapHttpClientPerHttpClientKey . put ( key , httpClient ) ; } else { if ( HTTPHC4Impl . log . isDebugEnabled ( ) ) { HTTPHC4Impl . log . debug ( ( ( ( "Reusing<seq2seq4repair_space>the<seq2seq4repair_space>HttpClient:<seq2seq4repair_space>@" + ( System . identityHashCode ( httpClient ) ) ) + "<seq2seq4repair_space>" ) + ( key . toString ( ) ) ) ) ; } } MeasuringConnectionManager connectionManager = ( ( MeasuringConnectionManager ) ( httpClient . getConnectionManager ( ) ) ) ; connectionManager . setSample ( res ) ;

Fix:
resolver = SystemDefaultDnsResolver . INSTANCE ;